56 MORPHOLOGY AND EVOLUTION
The vestibule of the mouth has diverticula known as cheek pouches in all except the Langurs and Guerezas. Externally the buccinator and platysma cover the pouch
on each side.
The stomach is a simple sac in those species which have cheek-pouches, but it is long and sacculated in the Langurs and Guerezas, which have no pouches. Possibly, as Owen suggested, the first compartment of the stomach replaces the pouches.
The caecum is conical and devoid of a vermiform appendix. The colon is sacculated by longitudinal muscle bands, and it is freer than in the higher Siiniidae.
The parotid and submaxillary salivary glands are large, but the sublingual glands are small. The pancreas shows nothing peculiar, and its duct opens along with the common bile duct into the duodenum.
The liver varies in size and position. Thus it is very small and pushed up into the left hypochondrium by the large stomach in the Guerezas. In the Cerco-pithecinae it lies across the middle line, and it is well developed. There are no bare areas between it and the diaphragm. The degree of subdivision into lobes varies, and the component lobes vary in size in different genera. Thus the two central lobes are fused in the Baboons, but separate in the Guerezas; and the left lateral lobe is large in the former, but diminutive in the latter. Caudate and Spigelian lobes are both present. The gall-bladder is superficial in some species, but deeply recessed in others.
Organs of Circulation.—The long axis of the heart is more vertical than in the Simiidse, and the azygos